Objective-C Programming: The Big Nerd Ranch Guide

Callbacks and object ownership

Inherent in any of these callback schemes is the risk of strong reference cycles. Often the object you create has a pointer to the object that is going to call back. And it has a pointer to the object you created. If they each have strong references to each other, you end up with a strong reference cycle – neither of them will ever get deallocated.

Figure 27.3  Strong reference cycle

Thus, it was decided that:

• Notification centers do not own their observers. If an object is an observer, it will typically remove itself from the notification center in its dealloc method:

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